1. Field of the Invention
The invention relates to a device for providing a liquid additive for exhaust-gas purification, which may be utilized in particular to supply a liquid additive, in particular a urea-water solution, to an exhaust-gas treatment device of a motor vehicle.
2. Detailed Description of the Prior Art
Liquid additives are required for example in exhaust-gas treatment devices in which nitrogen compounds in the exhaust gas are reduced with the aid of a reducing agent. In exhaust-gas treatment devices of this type, selective catalytic reduction (SCR) is implemented. Ammonia is used as reducing agent in the SCR method. Ammonia is often stored in motor vehicles not directly but rather in the form of a liquid additive that can be converted to form ammonia within the exhaust gas in the exhaust-gas treatment device and/or outside the exhaust gas in a reactor provided for the purpose. A liquid additive commonly used for the SCR method is a urea-water solution, which is available with a urea content of 32.5% under the trade name AdBlue®.
For the design of such devices, it must be observed that the liquid or aqueous additive can freeze at low temperatures. A urea-water solution freezes at a temperature of approximately −11° C. In the case of motor vehicles, such low temperatures may arise during relatively long standstill periods in winter. As it freezes, the liquid additive expands, wherein the device for providing the liquid additive can be damaged or even destroyed as a result. The volume expansion during the freezing process can cause ducts of a device of said type to deform or even rupture. For this reason, it is known, on a device of this type to provide protective measures, which as far as possible, substantially prevent damage and/or destruction of the device. For example, flexible or deformable elements are known that are arranged in the ducts of a device to accommodate a volume expansion during the freezing process. It is however a problem that such protective measures often exhibit low durability, and can nevertheless be damaged as a result of multiple or repeated instances of freezing of the liquid additive.